Note: Descriptions are shown in the official language in which they were submitted.
1 335 1 45
SINGLE COMPONENT, LATENT CURING EPO~Y RESIN COMPOSITION
This invention relates to a single component curing
epoxy resin composition having excellent storage time or pot
life which is composed of a polyepoxide, an isocyanate
compound and a heat activatable curing agent composed of a
5 crystallin~ salt of a polyamine and a polyhydric phenol.
Single component or one part latent curing epoxy
compositions based on curing agents such as boron
trifluoride amine complexes, dicyandiamide, melamine, etc.
are known in the prior art. ~hese prior art compositions
10 generally have problems of shelf life stability or require
high heat curing conditions and long periods of time for the
curing to take place.
U.S. Patent No. 3,519,576 describes the use of
polyphenate salts of a polyamine and a polyhydric phenol as
15 latent curing agents for epoxy resins. However, as can be
seen from the disclosure of this patent, the salts which
provide rapid curing of epoxy resins at moderately elevated
temperatures lack good shelf stability under ambient
conditions of storage and in order to obtain the shelf
20 stability of greater than three months for a one component
epoxy composition of a complex flavan derivative, amine salt
is used. The use of isocyanates in the mixture of the
polyepoxide resins with polyphenate salts of commonly
available polyamines and polyphenols to provide the one
25 part, latent curing epoxy compositions having long shelf
stability (greater than three months at ambient temperature)
with a rapid curing at moderately elevated temperatures has
never been disclosed in the prior art.
Many curing agents including polyamines, amido amines,
30 phenolics, thiols, polycarboxylic acids and anhydrides are
known in the prior art for curing epoxy resins to give
thermoset polymers which have been used in applications
including coatings, adhesives, reinforced plastics,
composites and the like. Mixtures of most commonly used
35 conventional amine curing agents with epoxy resins generally
have a short pot life; i.e., they remain free-flowing and
1- ~
,
- 2 - I 335 1 45
uncured for only a short tim~ at room temperature. For
instance, the commonly used aliphatic amine curatives
provide maximu~ pot life (open time or application time at
am~ient temperatures) of only a few hours (generally less
5 than five hours). For this reason, most epoxy compositions
are based on two-component systemsO Considerable efforts
have been devoted to developing single component epoxy resin
compositions containing latent curing agents which will have
a long pot life at room temperature, thus improving the
10 convenience of handling, storing and avoiding the mixing of
the resin compositions, but will cure rapidly upon heating
at moderately elevated temperatures. In this respect,
certain solid amines having high melting points and
substantially low solubility in epoxy resins; for instance,
15 melamine, dicyandiamide and the like, have been utilized in
single component curable epoxy compositions. The use of
such amines requires much elevated temperatures for longer
times for cure that are generally acceptable to those
working in the art. Many prior art reports are available
20 dealing with the use of certain accelerators for these amine
curatives for epoxy resins. For instance, U.S. Patents
3,903,048 and 4,459,393 make such disclosures. Other
latent curing agents disclosed in the prior art include
boron trifluoride amine complexes (U.S. Patent 2,717,885);
25 however, these complexes provide slow cures and are
corrosive, sensitive to moisture, and are not truly latent
because of a gradual release of the amine curative from the
complex or gradual cure of the epoxy resin by the complex
itself upon standing.
U.S. Patent 3,519, 576 discloses the use of certain
polyphenate salts of polyamines and polyhvdric phenols, as
latent curing agents. However, the polyphenates which are
obtainable from the more commonly available polyphenols and
polyamines cure epoxy resins readily at moderately elevated
35 temperatures (from about 80 degrees C. to about 150 degrees
C.) but have been shown to have poor pot life (shelf
stability at ambient temperatures) and thus are not
. ~ ~ 3 - 1335145
particularly useful in a single componen~ epoxy system.
For instance, the polyphenate salt of ethylene diamine and
Bisphenol-A which cures epoxy resins in approximately two
minutes at 120 degrees C. has been shown to have room
5 temperature shelf life of only one day.
The present invention provides one component, curable
epoxy compositions having shelf life superior to those
employing known latent curing resins which can be activated
at lower temperatures and which, once activated, will cure
lO to hard, tough solid products more rapidly than latent
compositions hitherto available. The one component latent
curing epoxy compositions of this invention comprise a
polyepoxide mixed with an isocyanate which can be a mono
isocyanate or a polyisocyanate and a polyphenate salt of a
15 polyamine and a polyhydric phenol. The improved shelf life
of the present epoxy compositions over those disclosed in
U.S. Patent 3,519,576 is believed to be due to the reaction
of isocyanate with partial primary or secondary amine of the
polyphenate thus probably behaving as an encapsulation of
20 the polyphenate salt, in situ, and thus making it less
soluble in the epoxy resin medium. The modified curing
agents of this invention melt rapidly and/or dissolve in the
resin composition upon moderate heating. Furthermore, these
curing agents provide more rapid cures compared to that of
25 free polyamines and this is believed to be due to the
synergistic effect of phenolic with amines and both
phenolics and amines undergo reaction with polyepoxides.
In order to demonstrate the significant improvement in
the shelf life of the epoxy compositions of this invention
30 exemplified by the salt of ethylene diamine and Bisphenol-A
and a small amount of a diisocyanate a shelf life of over
three months at room temperature was observed and the
composition still cured at 130 degrees C. within two
minutes. Without the isocyanate, the same composition was
35 found to have a shelf life at room temperature of only one
day. Another advantage of the compositions embodied in this
~ ~ ~ 4 ~ 1335145
in~ention is that the presence of small amounts of
isocyanates in them results in i~uvlng the thixotropic
properties of the total composition thus providing
non-sagging properties to the composition which is i~uyO Lant
S when one wishes to appLy the composition to verticaL or
other non-horizontal surfaces without concurrent running or
dripping of the composition before it is cured such as in
coating or adhesive applications.
E~y resins or polyepoxides suitable for use in the
10 pract~ce of this in~ention include those disclosed in U.S.
Patent ~os. 2,500,600 and 2,324,483.
Preferred in this invention are
1,2-epoxy compounds having an~epoxide equivalence greater
than 1, that is to say, compounds cont~ning more than one
15 group of the formt-l A
The 1,2-epoxide groups may be either tPrm;n~l or inner
ones. Particularly suitable t~m~ 1,2-epoxide groups are
1,2-epoxy ethyl or 1,2-epoxy propyl qroups. The latter may
be l;nk~ to an oxygen atom, that is to say, they are
glycidyl ether or glycidyl ester groups. Compounds with
25 inner epoxide groups usually contain the 1,2-epoxide group
in an aliphatic chain or in a cycloaliphatic r~ng.
A~ epoxy c~.uy~u~ds cont~;ning an inner 1,2-epoxy group
there are suita~le epoxidized diolefins, dienes, or cyclic
dienes, such as 1,2,5,6-diepoxy hexane, 1,2,4,5-diepoxy
30 cyCloh~xAn~, dicyclopentadiene diepoxide, dipentene
diepoxide, vinyl cyclohexene diepaxide, epoY;~i~ed
diole~inically unsaturated ca~Lu~ylic acid esters, such as
methyl-9,10,12,13-diepoxy stearate or the dimethyl ester of
6,7,10,11-diepoxvh~A~c~n~-1,16-dicarboxy~ic acid.
35 Furth~more, there may be mentioned epoxidized mono-, di-,
or polyester, and mono-, di-, or polyaceta7s cont~ining at
P~ .
' .
~ - 5 - l 335 1 45
least one cycloaliphatic 5-membered or 6-membered ring, to
which at least two 1,2-epoxidized groups are linked.
A widely used class of polyepoxides which can be used
in the present invention are the epoxy polyethers obtained
5 by reacting a halogen containing epoxide or dihalohydrin,
such as epichlorohydrin, epibromohydrin, 3-chloro-1,2-
epoxyoctane, and the like with either a polyhydric phenol or
a polyhydric alcohol.
The isocyanates useful in this invention include mono,
10 di and polyisocyanates which can be either aliphatic or
aromatic in nature. The amount of isocyanate used in the
compositions can vary from about 0.01 to 0.5 isocyanate
group per primary and/or secondary amine group present in
the polyamine used in the formation of the
15 polyamine-polyphenate salt.
The isocyanates useful in the compositions of this
invention include the aromatic and aliphatic monoisocyanates
such as phenyl isocyanate, tolyl isocyanate, cyclohexyl
isocyanate, tetramethylene xylene isocyanate, linear
20 aliphatic isocyanates and the like.
Polyisocyanates useful in this invention include
organic isocyanates having at least two isocyanate groups
per molecule. The polyisocyanates can be of low, high or
intermediate molecular weight and can be any of a wide
25 variety of organic polyisocyanates including ethylene
diisocyanate, trimethylene diisocyanate, dodecamethylene
diisocyanate, hexamethylene diisocyanate, hexamethylene
diisocyanate trimer, tetraethylene diisocyanate,
pentamethylene diisocyanate, propylene-1,2-diisocyanate,
30 2,3-dimethyl tetramethylene diisocyanate, butylene-1,2-
diisocyanate, butylene-1,3-diisocyanate, 1,4-diisocyanato
cyclohexane, cyclopentene-1,3-diisocyanate, p-phenylene
diisocyanate, 1-methyl phenylene-2,4-diisocyanate, naphthal-
ene-1,4-diisocyanate, toluene diisocyanate, diphenyl-4,4'-
35 diisocyanate, benzene-1,2,4-triisocyanate, xylene-1,4-
diisocyanate, xylylene-1,3-diisocyanate, 4,4'-diphenylene
- 6 - 1 3 3 5 1 45
methane diisocyanate, 4,4'-diphen~lene propane diisocyanate,
tetramethylene xylene diisocyanate, 1,2,3,4-tetraisocyanato
butane, butane-1,2,3-triisocyanate, polymethylene polyphenyl
isocyanate, and other polyisocyanates having an isocyanate
5 functionality of at least two which are more fully disclosed
in U.S. Patent Numbers 3,350,362 and 3,382,215. Polyiso-
cyanates which are polymeric in nature including isocyanate
prepolymers of all types are included in this invention.
Polyphenolic compounds useful in this invention may be
10 any compound having two or more aromatic hydroxyl or
phenolic groups per molecule and preferably are those
polyphenolic compounds which form crystalline salts with
polyamines. Representative polyphenolic compounds include
Bisphenol-A, Bisphenol-F, resorcinol, 2,2'- and
15 4,4-dihydroxy biphenyl, 1,5-dihydroxynaphthalene, p-p'-oxy
bisphenol, flavan derivatives, phenol/formaldehyde resins
(Novolac), 4,4'-sulfonyldiphenol, tetrachloro Bisphenol-A
and others.
The polyamines useful in this invention are those
20 compounds having more than one amino group per molecule and
they can contain any combination o~ primary, secondary and
tertiary amine groups. The polyamines may be aliphatic or
aromatic in nature and it is further required that at least
one of the amine groups be a primarv or secondary amine
25 group. Most preferred polyamines are those which when used
separately as curatives for epoxy resins are highly
reactive, providing rapid cures at room temperature. The
salts of polyamineS and polyphenolic compounds used in this
invention permit the used of reactive polyamines in latent
30 form which only become activated upon heating of the epoxy
resin composition for curing of same. Examples of such
highly reactive polyamines include ethvlene diamine,
propylene diamine, 1,6-hexamethylene diamine, mono and di
alkyl substituted ethylene or porpylene diam-ines, diethylene
35 triamine, triethylene tetramine, tetraethylene pentamine,
pentaethylene hexamine, dipropylene triamine, cyclohexane
1 335 1 45
diamine, bislaminomethyl3 cyclohexane, xylylene diamine,
piperazine, aminoethvl piperazine, bis(aminopropyl3
piperazine, isophorone diamine, dimer acid diamine, dimer
acid, triamine, and the like. Other useful polyamines will
5 be apparent to those skilled in the art. The polyphenate
salts of polyamines with polyhydric phenols are prepared in
about 1:1 molar ratio, however, in some instances the 1:2
salts are also formed. For instance, ethylene diamine forms
a 1:1 salt with Bisphenol-A, whereas bis(aminopropyl)
10 piperazine and triethylene tetramine form 1:2 salts with
Bisphenol-A.
Fillers, diluents, plasticizers, monoepoxides, and
modifiers and other additives of this type commonly know in
the art may be incorporated in the compositions of this
15 invention. There is no appreciable deleterious effect on
the shelf life of these systems so long as the additives are
not so7 vents for the polyaminophenate salts or the probable
reaction product of these salts with isocyanate.
The latent curing polyepoxide compositions of this
20 invention are useful in applications including adhesives,
coatings, laminating resins, composites, reinforced
structural materials, potting compounds, tooling and molding
compounds.
The compositions of this invention may be cured by
25 applying moderate heat, generally above about 80 degrees C.
and preferably in the range of from about 100 to 150 degrees
C.
This invention is further llustrated in the following
representative examples.
EXAMPLE 1
A solution of a liquid diglycidyl ether of Bisphenol-A
(epoxy equivalent weight of 185) containing 7.6% by weight of
isophorone diisocyanate was prepared and was found to have a
35 shelf stability of over three months at ambient temperatures.
A 15g portion of this material was mixed with 5g of finely
~ 8 _ l 335 1 45
powdered ~particle size smaller than 100 mesh) crystalline
solid adduct of ethylene diamine with Bisphenol-A prepared
by miY~ing equimolar amounts of a solution of ethylene
diamine with a solution of Bisphenol-A in a solvent such as
5 diethyl ether, methanol or toluene followed by separation
and drying of the crystalline adduct. The resulting
thixotropic paste was divided into two parts, the first part
of which was kept at room temperature for a shelf life study
and the second part was heated at 130 degrees C. at which
10 temperature curing occurred in one minute and 10 seconds to
give a hard solid polymer. This polymer, after post curing
at 130 degrees C for 30 minutes was found to have a Shore D
hardness of 84. The first part which was aged at room
temperature remained soft and ungelled even after three
lS months. After standing three months, the portion stored at
room temperature was heated to 130 degrees C. and gelation
occurred within one minute and 15 seconds at this
temperature to give a hard polymer which when postcured at
130C for 30 minutes was found to have a Shore D hardness of
20 85. This clearly demonstrates that the mixture of a
polyepoxide resin ard a solid polyphenate salt of ethylene
diamine and Bisphenol-A in the presence of polyisocyanate
has long shelf stability at ambient temperatures and is able
to cure rapidly at moderately elevated temperatures.
EXAMPLE 2
This example is for comparative purposes demonstrating
that in the absence of any isocyanate in the single
component epoxide resin composition the material has poor
30 shelf stability. The composition was prepare in accordance
with the teachings of U.S. Patent 3,519,576. The procedure
of Example 1 was followed using 15g of the liquid diglycidyl
ether of Bisphenol-A and 5g of the solid ethylene
diamine/Bisphenol-A adduct. The first portion which was
35 stored at room temperature was found to have a shelf
1 335 1 45
stability of less than a day giving a semi-solid material
and the second portion which was immediately heated at 130
degrees C. was found to cure in one minute and 10 seconds.
The solid polymer after post curing at 130C for 30 minutes
5 was found to have a Shore D hardness of 85. The shelf
stability of this composition at room temperature is in
agreement with the disclosure of U.S. Patent 3,519,576 which
shows relatively poor shelf stability of the mixture absent
the isocyanate which is essential in the compositions of the
10 present invention.
EXAMPLES 3-19
Several polyphenate salts of polyamines with
polyphenols were prepared by mixing the solutions of
15 polyamines with the solutions of polyphenols in appropriate
stoichiometries. These salts were mixed with the
polyepoxide resins either in the presence of small amounts
of polyisocyanates or in the absence of any isocyanate
materials for comparison purposes. The shelf life
20 stabilities and cure speeds of the compositions at
moderately elevated temperatures are listed in Table 1.
Example 5, 8, 10, 17 and 19 are for comparative purposes and
are otherwise outside the scope of the present invention.
It is apparent that the compositions devoid of isocyanates
25 consistently showed poor shelf stabilitv when compared with
those those having isocyanates present.
1 335 1 ~5
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335 1 45
EXAMPLE 20
A one part structur~l adhesive composition was prepared
by mixing 52.4 parts by weight of the liquid diglycidyl
ether of Bisphenol-A treated with 10% carboxylic acid
5 terminated butadiene/acrylonitrile (13% acrylonitrile) Hycar
rubber (BF Goodrich), 4 parts by weigllt of isophorone
diisocyanate, 3.1 part by weight of N-ethyl toluene
sulfonamide, 20.3 parts by weight of dry talc and 20.0 parts
by weight of powdered 1:1 adduct of ethylene diamine with
10 Bisphenol-A. This pasty material was applied in the form of
a ~-inch thick bead on a 12 inch long x 4 inch wide and 100
mils thick fiberglass reinforced polyester plastic (sheet
molding compound), at one end along the length of the SMC.
After sprinkling a few 30 mils diameter glass beads to
15 obtain a controlled 30 mils thick adhesive thickness,
another SMC sheet of sa~me dimensions as above was placed on
top of the adhesive bead, thus covering a one-inch wide
area. This was cured in a heated ~ixture at 230F for four
minutes under a contact pressure o~ 1 psi, followed by
20 postcuring at 280F for 30 minutes in an oven. One-inch
wide lap shear test samples were cut and tested in the
following manner:
A = Lap Shear Strength at RT
B = Lap Shear Strength at RT a~ter 400F/l hour postbake
C = Lap Shear Strength at 180F
The test results are listed in Ta~le 2. Adhesive bonds were
also prepared on unprimed cold rolled steel and tested in
30 lap shear mode which showed strength of approx. 1200 psi.
* Trade-mark
~ - 12 -
1 335 1 45
TABLE 2
Sample No. Test Procedure Lap Shear Strength (psi)
1 A 400 DL
2 A 430 DL
3 B 421 DL
4 B 370 DL
C 433 DL
6 C 448 CF/FT
DL = Substrate delaminated; CF/FT = Mixed cohesive failure
and fiber tear of SMC
